Lithium-ion batteries typically include an anode, an electrolyte, and a cathode that contains lithium in the form of a lithium-transition metal oxide. Such lithium-transition metal oxides typically include LiCoO2, LiNiO2 and Li(NiCo)O2. A lithium-transition metal oxide that has been proposed as a replacement for LiCoO2 is Liy[NixCo1−2xMnx]O2 which adopts the α-NaFeO2 type structure and can be regarded as the partial substitution of Ni2+ and Mn4+ (1:1) for Co3+ in LiCoO2. Liy[NixCo1−2xMn x]O2 materials prepared at 900° C. exhibit good cell performance and appear to be much less reactive with electrolytes at high temperatures compared to LiCoO2 when charged at high voltage. However, the material density and thus the resulting electrode density of samples previously reported are lower than required for many industrial applications of lithium-ion batteries.
Liy[NixCo1−2xMnx]O2 with x being in the range of 0.25 to 0.375 and y being in the range of 0.9 to 1.3 can deliver a stable capacity of about 160 mAh/g using a specific current of 40 mA/g when cycled between 2.5 V and 4.4 V. Because both nickel and manganese are less expensive than cobalt, Liy[NixCo1−2xMnx]O2 appears as a promising composition to replace LiCoO2. One undesirable feature of Liy[NixCO1−2xMnx]O2 compounds, however, is their low density achieved by the known synthesis of starting from a co-precipitation of hydroxides followed by a heat treatment at about 900° C. This undesirable low electrode density ultimately leads to low volumetric capacities in practical lithium-ion cells.
Denser oxides can be obtained using a synthesis constituted by a more controlled co-precipitation followed by treatment at temperatures greater than or equal to 1100° C. with a slow cooling to preserve cell performance. Such a synthesis, however, is not completely suitable for industrial applications because the controlled precipitation process is difficult and is expensive due to energy requirements to achieve the high heat treating temperatures. Also, oxides synthesized this way exhibit high first cycle irreversible capacity, thus limiting their useful capacity when used in a battery.
It is known in the art that LiF used in producing Li1+xMn2-x-yMyO4-zFz (with 0<x<=0.15, 0<y<=0.3, and 0<z<=0.3, and M is a metal comprised of at least one of Mg, Al, Co, Ni, Fe, Cr), can function as a flux for lithium ion electrode materials. The art recognizes that this compound has a spinel crystal structure. Further it is known in the art that a spinel structure requires the nominal ratio of lithium to transition-metal to oxygen in the compound of 1:2:4. LiF is incorporated into the crystalline structure, i.e., main phase, of the lithium transition metal oxide.
The art describes H3BO3 as a raw material in the synthesis of Li[(Ni0.5Mn0.5)1-x-yMxBy]O2 (where 0<=x<=0.10, 0<=y<=0.05, and M is one of V, Al, Mg, Co, Ti, Fe, Cu, Zn) which can be used as a positive electrode active material. The amount of Co in this compound can be up to 10 atomic percent of the amount of lithium in the synthesized lithium material. The art teaches away from increasing density of this material in the belief that increased density leads to inferior cell performance.